Localities

Principal localities:

History of Research

Brief history of research:

The concept of Elrathia permulta is quite confused. Walcott named the species Ptychoparia permulta in 1918 and illustrated two specimens, one clearly designated as the type. Resser (1937) noted that the illustrated specimens were quite different, moved both to Walcott's 1924 genus Elrathia, and proposed the name Elrathia dubia for the second species. Unfortunately, he based this on the original type of permulta; Rasetti (1951) declared dubia invalid, returned the type specimen to Elrathia permulta, and designated the other of Walcott's specimens as a paratype of Ehmaniella burgessensis. The holotype of permulta, however, lacks many of the diagnostic characters of Elrathia, and Robison (1964) suggested it represents a new genus.

Description

Morphology:

Hard parts: the adult dorsal exoskeleton is up to 25 mm long, with a large semicircular cephalon occupying about one-third the total length. The cephalon is bordered by a rounded rim and broad inner furrow; genal angles are produced into sharp triangular spines extending back to the fourth thoracic segment. There is a relatively long field between the narrow, tapered, and anteriorly rounded glabella and the frontal rim. Eyes are small and transverse eye ridges are very weak. Three pairs of shallow lateral furrows mark the glabella. The thorax comprises 14 segments, and tapers back more rapidly over the posterior half to a small rounded pygidium. The surface of the exoskeleton is variably granulate.